1. Field of the Invention
The present invention relates to an electrophotographic apparatus such as an electrostatic image transfer copying machine, a laser printer or the like.
2. Description of the Prior Art
FIG. 4 shows a conventional electrophotographic apparatus, in which the surface of a photoconductor 31 charged at a prescribed potential by a charger 32 is exposed to a laser beam 33 emitted from an exposure unit (not shown), resulting in an electrostatic latent image on the surface of the photoconductor 31 as a result of the potential difference between the exposed areas where the potential is reduced and the unexposed areas where the original potential is retained. The electrostatic latent image is developed into a toner image by means of a developer unit 34, the toner image then being transferred by means of a transfer charger 36 onto copy paper 35 fed from a paper feed unit (not shown). Thereafter, the copy paper 35 onto which the toner image has been transferred undergoes a fixing process by a fixing unit (not shown), and is discharged to the outside of the machine. The toner remaining on the surface of the photoconductor 31 after the transfer process is scraped off the surface thereof by means of a cleaning unit 37. The residual potential on the surface of the photoconductor 31 is removed by means of a discharge lamp 38 before the next copy cycle is performed.
The removal of the residual potential on the photoconductor 31 performed by the discharge lamp 38 after the transfer process is an indispensable process. Without the discharge process, the potential on the photoconductor 31 would continue to rise through repeated charge by the charger 32, eventually causing a dielectric breakdown of the photoconductor because of excessive charges.
On the other hand, the provision of a special discharge unit such as the discharge lamp 38 would constitute a disadvantageous factor with regard to reduction in the size and cost of the machine. Therefore, previously there have been proposed techniques that do not require the provision of a special discharge unit, which include, for example, a construction as disclosed in Japanese Laid-Open Patent Publication No. 56-16155 wherein a transfer charger is utilized for discharging the photoconductor, and a construction as disclosed in Japanese Laid-Open Patent Publication No. 59-105673 wherein a laser beam emitted from an exposure unit is split to discharge the photoconductor 31.
However, while both of the above-mentioned conventional constructions have been successful in eliminating the need for a special discharge unit, neither of them have been able to avoid the problems accompanying the reversal developing method, that is, carrier attraction and toner adherence to the photoconductor 31 after completion of an image forming operation. Such phenomena cause problems in the production of a good copy image.